Both Thunderbird and my ISP have junk mail filters. It would be really nice if Thunderbird could provide feedback to the ISP on what I think is spam. That is, when I designate a message as spam, Thunderbird sends the message and the spam designation to the ISP's spam filter. (Given that different ISPs use different spam filters, this would need to be done in some sort of universal way so that ISP filters from different developers could use this information.) There are two benefits to this. First, it would allow me to train the ISP's filter so that less spam reaches me. Second, assuming the ISP's spam filter uses messages from all users to determine what is spam (rather than on a per-user basis), it would allow the ISP's customers to collectively define what is spam, thereby reducing spam by more than any one individual user could do. Thanks.